There are cases that designs are printed on T-shirts, bathing suits, and the like by an ink-jet method in production of T-shirts, bathing suits, and the like having original designs. In the case where a ground color of a T-shirt or the like is white, a printing may be performed without a pretreatment. In contrast, in the case where the ground color is deep such as black, it is necessary that a design is printed after a discharge-printing treatment. For the discharge-printing treatment, a dedicated discharge-printing treatment agent is used. Many of discharge-printing treatment agents are two-pack type discharge-printing treatment agents each composed of two types of treatment agents. In the two-pack type discharge-printing treatment agent, one of the two types of treatment agents is a reducing treatment agent. Therefore, each of the two types of treatment agents is stored in a different container, and in use, a discharge-printing treatment agent is prepared by mixing the two-types of them.